Fire doors have long been used for providing safety mechanisms to protect an environment were an event such as the actuation of a fire alarm or smoke detector occurs. Systems which utilize fire doors generally receive their operating power from the electrical system of a building. When an alarm event occurs or the operating power is lost, a release mechanism interfaced to the fire door causes the fire door to close, thereby protecting the environment from the fire condition and smoke.
A fire door system usually comprises a rolling fire door assembly that includes a rolling fire door mounted on a horizontally extending axle for movement of the door between the raised (and lowered) positions. See, for example, U.S. Pat. No. 5,082,316, Wardlaw, at column 2, lines 17-28, the teachings of which are specifically incorporated herein by reference.
In these systems, the fire door is maintained in the raised position by a release mechanism which is mounted on the wall above the door. Release mechanisms are connected to release levers through a chain so that the release lever is held in locking engagement when the chain is in tension. The chain normally comprises a fusible link which is adapted to melt and thereby release the door in response to the heat produced by a fire.
There are many types of release mechanisms known in the art, examples of which are disclosed in the Wardlaw patent referenced above. Generally, a release mechanism and its associated detection system may be adjusted to compensate for more or less severe ambient temperature changes by different settings of the release mechanism, or by varying the size of compensating vents in the system to increase or decrease the rate of pressure buildup caused by a sudden temperature rise. Such release mechanisms may also be "time-delay release devices" in that they only release the fire door to close during emergency conditions after a predetermined time delay which is initiated after receiving data about an emergency condition, or after losing operating power.
Prior release devices have also generally used solenoids to interface with the temperature fuse link system and chain which drives the rolling fire door. The solenoids actuate the chain during the alarm or power loss condition. The release devices are termed "fail safe" when the solenoid operates or when the operating power to the system is lost.
However, the prior release mechanisms known in the art have not possessed the ability to operate for a period of time to sense an alarm condition when operating power is lost. This has resulted in fire doors being closed only on the condition when operating power is lost but when no fire or other emergency event is detected. Thus when power is interrupted to the release device in response to some non-catastrophic or non-fire condition, it is generally not necessary for the rolling door to close. The prior rolling doors and release mechanisms have automatically closed in this situation, thereby presenting potential dangers to individuals who might be trapped in a building without power, and further requiring resetting of the fire control system. The rolling fire door art has not heretofore devised a solution to these problems.